issue contents

ISSN: 2053-2733

November 1999 issue

Highlighted illustration

Cover illustration: One quadrant of each of four fibre diffraction patterns from disordered polynucleotide fibres. The patterns were calculated for fibres with disorder as follows. Upper left: crystalline (no disorder); upper right: noncrystalline (completely disordered); lower left: discrete rotational disorder and correlated lattice disorder; lower right: random screw disorder. See Stroud & Millane [Acta Cryst. (1996), A52, 812-829].

research papers

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A method is derived from indexing the diffraction patterns of approximant structures from the N-dimensional indexing of the parent quasicrystal. Examples are given for the case of the approximant of the icosahedral phases with special emphasis on the origin of the so-called `systematic accidental' extinctions observed in pentagonal phases.

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Probabilistic formulas for estimating structure factors with indices of mixed type (some are integers and some half-integers) are given. The concept of `quasi-invariant' is fixed.

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The program SIR99 is a versatile tool for direct solution and complete refinement of small and large crystal structures.

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X-ray interference patterns from a finite perfect crystal have been studied theoretically using diamond as a model system.

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Debye–Waller factors for 19 compounds with the sodium chloride structure are given over a temperature range from 1 to 1000 K where appropriate.

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An off-axis ring pattern was observed in the 〈1\bar{1}1〉 zone-axis CBED pattern of NiO, and the pattern was interpreted using a two-Bloch-wave approximation.

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The change of structure-factor phases of several weak reflections of GaAs has been measured by three-beam interferences. Using a modulation technique, phase variations of the order of 1° for a field strength of 1 kV mm−1 were determined.

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Non-uniqueness of the multipole refinement of the electron density in ammonium dihydrogen phosphate and consequences on the topology of the electron density.

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Algebraic expressions for projection operators and symmetry-adapted functions (SAFs) of the icosahedral group for spinor (double-valued) representations are found by using the double-induced technique and eigenfunction method.

short communications

book reviews

Acta Cryst. (1999). A55, 1062
doi: 10.1107/S0108767399011939

international union of crystallography

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